I really like the look of delicately layered necklaces. It not only looks cool but its a great way to re-purpose items you already have. You can really start to see your necklaces in a different light: as part of a group instead of just a stand alone piece.
For this group, we combined different styles and lengths of chain but we kept the colors consistent in bright silver and black onyx.
A good way to start is to find a short, medium and long necklace that have something in common, whether its color, metal color, or gemstone color. Layer them on and see how they hang all together. It might take some experimenting but it might lead to something great!